\section{Proposed 3D Compact Model Standard}\label{sec:future}
Based on the previous works on 3D electrical characteristic modeling, our proposed 3D compact model includes three levels of models in terms of accuracy and complexity.

The first level of the model contains simple RLC model of TSV without considering any skin effect. This RLC model can provide us with the rough circuit performance estimation in a short time. Since skin effect is important at high frequencies, the accuracy level of this model is the lowest one. Based on the closed-form expressions given in section \ref{sec:level1}, the RLC value of TSVs can be easily computed at DC and low frequencies. For higher frequencies, compensation from simulation will be added to the model to make up the large error. Moreover, the TSV structure in the model can be customized for three kinds of cylindrical structures: without landing pad, with one landing pad and with two landing pads. 

The second level of this model considers various effects in TSV high frequency operations, such as skin effect, eddy current effect, and TSV coupling effect. For high frequency simulation, the complex RLCG model which is illustrated in section \ref{sec:level2} is adapted. As for low frequency circuit simulation, a modified simple RLC model combining the coupling C, L is used. The model in this level can provide a balance tradeoff between accuracy and simulation speed.

The last level consists of both complex model from last level and the temperature-dependent RLC model. Design time RLCG circuit simulation is not sufficient for performance prediction due to the temperature variation. So circuit simulation with thermal consideration and power consumption is closer to real cases. However, the existing temperature-dependent RLC model is still immature, and the new model development is required, especially for 2.5D circuits. Our first work in this level is to build a mature temperature-dependent RLC model for both 3D and 2.5D circuits and then merge this model with the RLCG model for thermal-aware complex circuit simulation.

In all the three model levels, RC models for RDL, BEOL, and micro-bump are included in case of full package simulation. Primary models of these three components are adapted from models that are introduced in section \ref{sec:others}, however further verification for model accuracy is needed.